Profile Modification and Irrigation Effects on Yield and Water Use of Wheat

Where water is limited, there are continuous searches for management practices that increase water use efficiency (WUE). Profile modification (PM) of Pullman clay loam (fine, mixed, thermic Torrertic Paleustolls) has been shown to increase yield and WUE of grain sorghum [ Sorghum bicolor (L.) Moench] and alfalfa ( Medicago sativa L.). We hypothesized that it might increase those of winter wheat ( Triticum aestivum L.) and, combined with limited irrigation, might further increase water use efficiency. A 4‐yr study was conducted on a site on which PM treatments (imposed in 1964) included thorough mixing of the soil profile to 0, 0.9, and 1.5 m with a wheel‐type ditching machine. Measurements in 1985 showed that PM still affected infiltration rate, bulk density, and surface elevation of the soil. Irrigation treatments were: (i) fall irrigation only (preplant or preplant + emergence), (ii) fall irrigation plus one spring irrigation, (iii) fall irrigation plus two spring irrigations, and (iv) fall irrigation plus three spring irrigations. Under irrigation Treatment I, compared to yields on unmodified soil, average grain yields were increased 11% by 0.9‐m PM and 20% by 1.5‐m PM. With Treatment II, average increases were 16 and 25%, respectively, but under treatments III and IV, PM did not affect grain yields. Under irrigation Treatment I, compared to WUE on unmodified soil, WUE for grain production was increased 10% on 0.9‐m PM soil and 16% on 1.5‐m PM soil. Under Treatment II, the respective increases were 15 and 21%, but with treatments III and IV, PM had little effect on WUE. Profile modification‐induced increases in wheat grain yield and WUE were small compared to those obtained with grain sorghum and alfalfa in previous studies. Profile modification of Pullman clay loam is not a feasible practice for wheat production because of limited yield response and high energy requirements to accomplish PM.